Cast epoxy bushing having a weldable flange

ABSTRACT

An electrical bushing assembly having an electrical conductor extending through a solid body member cast of insulating material, a rigid metallic mounting member or flange having a generally circular opening therein, a certain portion of said flange adjacent to the opening being embedded in said cast body member, and a cylindrical-shaped, thin, less rigid metallic member attached to said flange adjacent to the opening therein. The less rigid metallic member is completely embedded in the resin of the body member. The bushing assembly is mounted in sealed relationship to a casing enclosing electrical apparatus and fluid dielectric by welding the rigid mounting member or flange to the casing.

United States Patent 11 1 11 3,775,547 Woods [45'] Nov. 27, 1973 [54] CAST EPOXY BUSHING HAVING'A 793,974 4/1958 Great Britain 174/142 wELDABLE-FLANGE 806.955 1/1959 Great Britain 174/142 817,785 8/1959 Great Britain 174/142 [75] Inventor: Edmund E. Woods, Sharon, Pa.

[73] Assignee: Westinghouse Electric Corporation, Primary ExaminerLafamie Askin Pittsburgh, Pa. Attorney-A. T. Stratton et al.

[22] Filed: Oct. 12, 1972 21' A 1 N 297111 I [57] ABSTRACT l 1 pp o" An electrical bushing assembly having an electrical conductor extending through a solid body member [52] US. Cl. 174/152 R, 174/142 t f insulating material, a rigid metallic mounting [51] Int. Cl. H0lb 17/30 ber or flange having a generally circular opening [5 8] Field of Search 174/18, 142, 143, th i a rt i rtion of said flange adjacent to the l74/152 153 167 openingbeing embedded in said cast body member, and a cylindrical-shaped, thin, less rigid metallic mem- 1 1 References Clied ber attached to said flange adjacent to the opening UNITED STATES PATENTS therein. The less rigid metallic member is completely 3,504,106 3 1970 Keto 174/152 R embeddedin the resin Ofthe body membei- The bush" 9,652,975 3 1972 Keto 174/152 RUX ing assembly is mounted in Sealed relationship to 9 1,526,023 2/1925 Steinberger 174/142 X casing enclosing electrical apparatus and fluid dielec- 3,318,995 5/1967 Buckley et a1... 1,74/142 tric by welding the rigid mounting member or flange FOREIGN PATENTS OR APPLICATIONS casmg- 342,416 10/1921 vGermany 174/ 142 10 Claims, 4 Drawing Figures sz L18 ratus in many different ways, with the specific arrangement selected being determined by such factors as cost, application and intended environment of the apparatus. Regardless of the mounting arrangement selected,

all of them must mechanically secure the bushings through an opening in the casing, while providing and maintaining a fluid tight seal between the casing and the bushing, or'between the bushing conductorand the insulating body portion of the bushing. Further, an insulating fluid in the casing; such as oil, must not leak out of the apparatus through any of these locations.

' Sin'cethe end of the insulating bushing may be below the level of the insulatinglfuid, the interface between the conductor and the insulating body portion is particularly susceptible'to fluid leaks.

In prior art cast resins bushings, it has been the practice to cast a metallic mounting member or flange into the resin body portion of the bushing. The bushing is then disposed in'an'openingin a metallic casing, and then the metallic flange is welded to the casing. This arrangement is excellent for obtaining a good mechanical structure and for insuring that there are no leaks between the mounting" flange and the casing, butfluid leaks develop between the mounting flange and the cast body portion of the bushing, even when a gasket in the form of a resilient coating is applied to the mountingflange and 'cured or vulcanized, before it is embedded in the castsolid insulating material, because the welding heat damaged the bond between the coating and the mounting member, or between the coating and the cast solid insulation. Thus, it is desirable to be able to weld metallic mounting members or flanges to metallic casings, without permanently impairing the seal between the metallic mounting flange and the cast body portion of the bushing.

Prior art solved this problem by using a thermoplastic or elastomeric coating applied to the area of the flange which was embedded in the main cast body of the epoxy bushing. The reasons for this coating were twofold. First, to act as a cushion to prevent the resin ecapsulant from cracking due to mechanical stress set up during shrinkage of the resin ,onto the edge of the flange. Secondly, to act as a sealant to prevent the insulating fluids within the bushing assembly from leaking past the interface between the resin and the embedded flange. See as examples of prior art U.S. Pat. No. 3,504,106, issued to Keto, and U.S. Pat. No. 3,388,212, issued to Nichols.

Although these prior art devices provided an improvement over the previous prior art, problems were still encountered in that damage to the sealant by heat generated during welding still occurred and allowed leakage of fluid or loss of pressure in the bushing.

2 SUMMARY OF THE INVENTION The present invention discloses a structure wherein a rigid metallic mounting member, or flange, is embedded into an epoxy or other resinous body member and forms a leak-free and pressure-tight seal without the need for a thermoplastic or an elastomeric coating being applied to the embedded portion of the metallic mounting flange.

The basic flange construction of theprior art is re tained, but instead of applying such an elastomeric or thermoplastic coating, a thin, less rigid, metallic member, substantially cylindrical in. shape, is attached, by

weld or other suitable means, to the embedded portion of the rigid metallic mounting member. This thin, less rigid, metallic member may-be treated with an epoxy or othersimilar enamel or such treatment that will promote adhesion between it and the encapsulant resin material. The object of disposing such a thin, less rigid, metallic member in the cast insulating body member is to provide an alternative method of preventing leakage of fluid or loss of pressure of the bushing assembly.

An advantage of this invention is that it is possible to eliminate the need for any thermoplastic or elastomeric coating or sealant that was required by the prior art in order to obtain a leak-free and pressure-tight bushing. This invention also eliminates possible damage to the bushing by heat generated during welding. The thin metallic member is flexible enough so that it moves with the encapsulating resin as the resin shrinks during gellation, thus eliminating any possible. high mechanical stress areas which could cause cracking or breakage of the bond between the thin metallic'member and the encapsulatingresin. A further advantage is that, being a thin membrane, the thin metallic member conducts heat very rapidly into its surrounding media, thus reducing the possibility of breakage of the bond between the thin metallic member and the encapsulant should excessive heat be applied during welding.

The total effect of utilization of the teachings of this invention would be to provide a pressure-tight and leak-free bushing assembly, without the use of elastomeric or thermoplastic resinous material being disposed on that portion of the metallic mounting member which is embedded in the cast resinous body member. The elimination of the need for such thermoplastic or elastomeric resin leads to a simplification of manufacture and reduction or elimination of manufacturing erros which result under the conventional sealing method.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and uses of the invention will become more apparent when considered in view of the following detailed description and drawings, in which:

FIG. 1 is an elevational view, partially in section, of an electrical bushing constructed according to the teachings of this invention;

FIG. 2 is an elevational view, partially in section, of another embodiment of the invention;

FIG. 3 is an elevational view, partially in section, of still another embodiment of the invention; and,

FIG. 4 is an elevational view, partially in section, of yet another embodiment of the invention.

DESCRIPTIONOF THE PREFERRED EMBODIMENT filledepoxy resin, a first rigid metallic mounting member or flange l8, and a second less rigid metallic member 12.

Body memeber 16 has first. and second ends 17 and 19, respectively, and may be cast of anysuitable resinous insulation material which has the following characteristics. It must be'a good electrical insulator, weather resistant, crack resistant, rigid but not brittle. It must possess a high physical strength at. ambient and elevated temperatures, and it must have a coefficient of thermal expansion which closely matches the coefficient of thermalexpansion of the electrical conductor means 14. Body member 16 is preferably cast, instead of being molded, because of the superior strength of cast resinous insulation systems over molded systems. In general, the filled epoxy cast resin systems will provide the desired characteristic, with thefiller being selected to match the coefficient of thermal expansion of the filled resin system to that of the electrical conductormeans. A finely divided filler, suchas quartz or silica flour, has been found to be excellent in matching resin system to copper. For .7200 volt applications where the encased end of a bushing assembly is disposed in oil, or other insulating dielectric fluid,.fillers for providing arc and track resistance are usually not required. If the encased end is to be operated in air, freely divided alumina trihydrate (Al O '3l-I O) may be added to obtain the desired arc and trackr'esistance.

The conductor 14 may be solid, as illustrated, or a walled tube, having an external end 20 adapted for connection to an external electrical circuit, and an internal end 22, immersed in a dielectric fluid or vacuum 24. The internal end 22 is connected to electrical apparatus housed in casing 28.

The first rigid metallic rnounting member 18 has a generally circuit shaped central opening 21 therein defined by its flange or curved edge 25. The first rigid metallic mounting member has a predetermined continuous portion thereof adjacent to the opening 21 therein embedded in the insulating body member 16.

The first rigid metallic mounting member 18 may be formed of any suitable material, such as steel, copper, or aluminum, and is adapted for welding about its periphery by means of its flange 23 to the flange 27 of the casing 28 of the associated electrical apparatus, as illustrated by the welding bead 30. The metallic mounting member 18 is provided from metal having a thickness of approximately l/l6 of an inch and is considered to be a relatively inflexible or rigid member.

The second metallic member 12, having less rigidity than the first metallic mounting member 18, is attached to the first metallic mounting member 18 adjacentto 4 the opening 21 in the first metallic mounting member 18, as illustrated by the weld bead 32. The second metallic member 12 is substantially cylindrical in shape, and is completely embedded in the insulating body member 16. The metallic member 12 extends'from its attachment to the first rigid metallic mounting member 18 for a substantial distance, such direction being substantially parallel to the electrical conductor means 14. The second metallicmember 12 is a thin metallic membrane from 0.002 to 0.010 inch in thickness. The metallic member 12, may be constructed from steel, copper, aluminum, or any other suitable metal. The thinness of the second metallic member 12 permits the second metallic member 12 to be of sufficient flexibility so as to move with the insulating body member 16 as it shrinks or contracts during fabrication. It is important that metallic member 12 have less rigidity than the first rigid metallic mounting member 18, so that the metallic member 12 might flex and move with the resin body member 16 when the body member 16 expands and contracts without damaging the joint between the metal members 12 and 18. The second metallic member 12 is thin enough so that as to readily conduct heat to its surrounding media. Disposed on the second metallic member is a resinous material 34, such resinous material being utilized to cast the body member 16 so as to facilitate a bond between the second metallic member 12 and the insulating body member 16.

The second metallic member 12 is so attached to the first rigid metallic mounting member 18 and so disposed within the insulating body member 16 so as to eliminate the need for any thermoplastic or elastomeric sealant to make the electrical bushing assembly 10 leak-free and pressure-tight. The purpose of the second metallic member 12 being so disposed within the insulating body member 16 is to necessitate a longer'path for any fluid encased within bushing 10. which seeks to escape from bushing 10 by passing to the flange of the mounting member 18 and along the interface between the flange 18 and resin body member 16 to the outside of the bushing.

A release material 36 is disposed over a portion of the electrical conductor means 14 which permits the electrical conductor means 14 to move with respect to the insulating body member 16 over most of the length of the electrical conductor means 14 when the electrical conductor means 14 expands or contracts due to thermal cycling. The release material 36 is disposed on the fluid side of the bushing. A suitable release material is silicone grease.

FIG. 2 is an elevational view, partially in section, of another embodiment of this invention. In this view, electrical bushing 10 is shown as having its first rigid metallic mounting member 18 disposed at an inward and upward angle with respect to the electrical conductor means 14. The second metallic member 12 is disposed so as to extend from the attachment of second metallic member 12 with first rigid metallic mounting member 18 in a direction substantially parallel to the electrical conductor means 14.

FIG. 3 shows an elevational view, partially in section, of still another embodiment of the invention. In this view the electrical bushing assembly 10 is shown as having its first rigid metallic mounting member 18 disposed so as to form an inward and upward angle with the direction of said electrical means 14 and the second metallic member 12 is disposed so as to form an angle In summary, the advantages of having the second metallic member 12 attached-to thefirst rigid metallic mounting member 18, all completely embedde'd'within said insulatingbody member 16, is to eliminate the needfor any thermoplasticor elastomeric sealant. In

the priorart such sealant was necessary so as to render the electrical bushing assembly leak-free and pressure-tight. Utilizing the teachings of this invention and the disposition of the second metallic member 12, the need for such thermoplastic or elastomeric material is eliminated. Asa result, any manufacturing error which heretofore would have rendered the electrical bushing assembly 10 defective due to'leakage of the insulating dielectric fluid is eliminated. The thinnessof the second metallic member 12 permits a rapid conduction of any excess heat generated by welding the external flange 23 of the first rigid metallic mounting member 18 to the casing flange 27 of the electrical casing 28 into the surrounding media. Such rapid conduction of heat will prevent the breaking of any bonds formed between the second metallic member 12 and the insulating body member 16 due tothe presence of the resin 34. Also, the second metallic member 12 is flexible enough so that it is able tomove with the encapsulating resin of the insulating body member 16 as the insulating body member 16 shrinks during gellation of the insulating body member 16 thus eliminating'any possible high mechanical stress areas which could cause cracking or breakage of the bond between the second metallic member 12 and the encapsulating resins of the insulating bodymember l6.

Since numerous changes may be made in the abovedescribed apparatus and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 7

1 claim as my invention:

1. An electrical bushing assembly for mounting on a casing containing oil dielectric with aportion of said bushing assembly extending into said oil dielectric, said bushing assembly comprising:

an insulating body member formed of solid insulation,

electrical conductor means extending centrally and axially through said body member,

a release material disposed about a predetermined portion of said electrical conductor means adjacent said oil dielectric,

afirst rigid metallic mounting member having an opening therein, said first rigid metallic mounting member having a predetermined continuous portion around its opening embedded in said insulating body member,

a second thin and flexible metallic foil member attached to said first rigid metallic mounting member continuously about said opening therein with a fluid-tight seal, said second thin and flexible metallic foil member surrounding in spaced relationship a predetermined portion of said electrical conductor means, I

a resin material disposed about said second thin and flexible metallic foil member, said resin material bonding said thin and flexible metallic foil member to said solid body member with a fluid-tight seal, "said second thin and flexible metallic foil member extending from said fluid-tight seal with said first rigid metallic mounting member and being completely embedded in said insulating body member. 2. The electrical bushing assembly of claim 1 wherein said second thin and-flexible metallic foil member extends from said fluid-tight seal with said first rigid metallic mounting member in a direction substantially parallel to said conductor means.

3. The electrical bushing assembly of claim 1 wherein said second thin and flexible metallic foil member extends from said fluid-tight seal with said first rigid metallic mounting member in a direction substantially perpendicular to said first rigid metallic mounting member and substantially parallel to said conductor means.

4. The electrical bushing assembly of claim 1, wherein said second thin and flexible metallic foil member is substantially cylindrical in shape.

5. The electrical bushing assembly of claim 1 wherein said second thin and flexible metallic foil member is disposed so as to extend from said fluid-tight seal with said first rigid metallic mounting member in one direction.

6. The electrical bushing assembly of claim 1 wherein said second thin and flexible metallic foil member is disposed so as to extend from said fluid-tight seal with said first rigid metallic mounging member in one direction, said direction being substantially perpendicular to said first rigid metallic mounting member and substantially parallel to said conductor means.

7. The electrical bushing assembly of claim 1 wherein said second thin and flexible metallic foil member is disposed so as to extend from said fluid-tight seal with said first rigid metallic mounting member in two directions from its attachment to said first rigid metallic mounting member. 7

8. The electrical bushing assembly of claim 1 wherein said second thin and flexible metallic foil member is 10. The electrical bushing assembly of claim 9, V

wherein said second thin and flexible metallic foil member is fabricated of a material having a thickness within the limits of 0.002 to 0.010 of an inch. 

1. An electrical bushing assembly for mounting on a casing containing oil dielectric with a portion of said bushing assembly extending into said oil dielectric, said bushing assembly comprising: an insulating body member formed of solid insulation, electrical conductor means extending centrally and axially through said body member, a release material disposed about a predetermined portion of said electrical conductor means adjacent said oil dielectric, a first rigid metallic mounting member having an opening therein, said first rigid metallic mounting member having a predetermined continuous portion around its opening embedded in said insulating body member, a second thin and flexible metallic foil member attached to said first rigid metallic mounting member continuously about said opening therein with a fluid-tight seal, said second thin and flexible metallic foil member surrounding in spaced relationship a predetermined portion of said electrical conductor means, a resin material disposed about said second thin and flexible metallic foil member, said resin material bonding said thin and flexible metallic foil member to said solid body member with a fluid-tight seal, said second thin and flexible metallic foil member extending from said fluid-tight seal with said first rigid metallic mounting member and being completely embedded in said insulating body member.
 2. The electrical bushing assembly of claim 1 wherein said second thin and flexible metallic foil member extends from said fluid-tight seal with said first rigid metallic mounting member in a direction substantially parallel to said conductor means.
 3. The electrical bushing assembly of claim 1 wherein said second thin and flexible metallic foil member extends from said fluid-tight seal with said first rigid metallic mounting member in a direction substantially perpendicular to said first rigid metallic mounting member and substantially parallel to said conductor means.
 4. The electrical bushing assembly of claim 1, wherein said second thin and flexible metallic foil member is substantially cylindrical in shape.
 5. The electrical bushing assembly of claim 1 wherein said second thin and flexible metallic foil member is disposed so as to extend from said fluid-tight seal with said first rigid metallic mounting member in one direction.
 6. The electrical bushing assembly of claim 1 wherein said second thin and flexible metallic foil member is disposed so as to extend from said fluid-tight seal with said first rigid metallic mounging member in one direction, said direction being substantially perpendicular to said first rigid metallic mounting member and substantially parallel to said conductor means.
 7. The electrical bushing assembly of claim 1 wherein said second thin and flexible metallic foil member is disposed so as to extend from said fluid-tight seal with said first rigid metallic mounting member in two directions from its attachment to said first rigid metallic mounting member.
 8. The electrical bushing assembly of claim 1 wherein said second thin and flexible metallic foil member is disposed so as to extend from said fluid-tight seal with said first rigid metallic mounting member in two directions from its attachment to said first rigid metallic mounting member, said directions being substantially perpendicular to said first rigid metallic mounting member and substantially parallel to said conductor means.
 9. The electrical bushing assembly of claim 1, wherein said first rigid metallic mounting member is fabricated of a material approximately 1/16 of an inch thick.
 10. The electrical bushing assembly of claim 9, wherein said second thin and flexible metallic foil member is fabricated of a material having a thickness within the limits of 0.002 to 0.010 of an inch. 